As a result both trees are still looking quite good.
I moved my head so I could see better and a small furry creature was indeed sitting in the tree.
I have no idea how I had not noticed this quince before, but there it is, the Quest for a Quince is over. Buying Quince Minor clearly worked as a threat as it made Quince Minor get its act together. It was not through cross-pollination of these self-fertilising quinces as Quince Minor had no surviving blossom following the frosts.
So I hereby give you notice; I will complete the year following the quinces, but next year I shall move on and find a new tree to bother.
More trees being followed can be found here courtesy of Squirrelbasket.